JavaWeb HttpSession应用

package com.xzit.erpmodel.listeners;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
/**
 * 监听HttpSession 公共监听器
 * @author zengy
 *
 */

public class HttpSessionListenerImp implements HttpSessionListener {

    @Override
    public void sessionCreated(HttpSessionEvent arg0) {
        // TODO Auto-generated method stub
        HttpSession sess = arg0.getSession(); //获取新建的Session对象
        ServletContext context =  sess.getServletContext();    //获取ServletContext上下文对象
        
        Object obj = context.getAttribute("onlineNum");    //获取ServletContext上下文域中存储在线人数的属性
        if(obj == null) {
            context.setAttribute("onlineNum", Integer.valueOf(1)); //这是第一个登录成功的人
        }else {
            //在线人数增加1
            context.setAttribute("onlineNum", Integer.valueOf(Integer.parseInt(obj.toString()))+1);
        }
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent arg0) {
        HttpSession sess = arg0.getSession(); //获取新建的Session对象
        ServletContext context =  sess.getServletContext();    //获取ServletContext上下文对象
        
        // TODO Auto-generated method stub
        Object obj = context.getAttribute("onlineNum");    //获取ServletContext上下文域中存储在线人数的属性
        context.setAttribute("onlineNum", Integer.valueOf(Integer.parseInt(obj.toString()))-1);
    }

}

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8" import="com.xzit.erpmodel.users.domain.*"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jstl/core_rt" %>
        
    

    
    
    

class="f_0">
    class="hand">
        快 速 留 言 |&nbsp;
        个 人 中 心 |&nbsp;
        留 言  管 理 |&nbsp;
        总 部 门 户 |&nbsp;
        会 议 信 息 |&nbsp;
        资 源 中 心 &nbsp;
        
          &nbsp;
          &nbsp;
          &nbsp;
     &nbsp;    
    <%
        Object obj = session.getAttribute("currentUser");
        SysUsers user = null;
        if(obj != null){
            user = (SysUsers)obj;
            %>
        当前用户:
        class="hand">
        【<%=user.getName()%>】
         &nbsp;
        <%
            if(session.isNew()){
                %>
                     &nbsp;首次光临
            <%}
        %>
            
        
        
         &nbsp;
        <%
            Object lineNum = application.getAttribute("onlineNum");
            if(lineNum != null){%>
                
                当前在线用户<%=lineNum%>人
            <%}
        %>
        class="hand" style="color:graytext;">
            退出系统
           &nbsp;
        <%    
        }else{%>
            未登录   &nbsp;
        <%}
    %>

<?xml version="1.0" encoding="UTF-8"?>

  erpmms
  
  
  
        10
  
  
  
      class>com.xzit.erpmodel.listeners.HttpSessionListenerImpclass>
  
  
  
    login.jsp